Surface hardened cast iron article of manufacture



Patented Aug. 29, 1933 UNITED STATES PATENT OFFICE SURFACE HARDENED CAST IRON ARTICLE OF MANUFACTURE Delaware No Drawing. Application June 13, 1931, Serial 4 Claims. (01. 148-31) My invention relates to the surface hardening of articles made of cast iron alloys, the hardening being effected by the action of nitrogen-containing compounds, for example ammonia.

It is known that when a cast iron containing a small proportion of an alloying addition, such as one or more of the elements aluminum, silicon, manganese, chromium, nickel, cobalt, vanadium, molybdenum, tungsten, titanium and zirconium, is subjected toa nitriding. treatment, i. e., is heated at a moderate temperature in contact with ammonia or another nitrogen-liberating'compound, a beneficial hardening effect is produced. However, while the nitride hardening effect obtained by introducing the various elements above mentioned into cast iron is always very much superior to that of an ordinary cast iron, such hardening effect and the other resulting treatment vary considerably, depending upon the proportion of the alloying addition and the particular alloying element or elements comprising such addition. Consequently, cast iron alloys of these general types vary considerably in their suitability as regards their application for 'various industrial uses. Moreover, certain of the alloying elements mentioned tend to impart to the cast iron alloy product disadvantageous properties from the standpoint of casting and machinability.

I have found that cast iron alloys containing certain combinations of the alloying elements above mentioned exhibit exceptionally good properties as regards ability to acquire a high nitride hardness, toughness of the core and of the nitrided case, and improved properties as respects casting and machinability.

More specifically, I have found that cast irons containing from 2.0 to 4% of carbon, 1% or less each of silicon and manganese, and as alloying additions up to 1.85% aluminum and a small but effective proportion, not exceeding 0.5% of each, of any one or more of the elements chromium, vanadium and titanium, arecharacterized by especially good properties as regards their ability to be hardened by nitriding. Cast irons falling within this range of proportions may be classed as white cast irons. They are relatively hard in their 'cast state but may be worked with tools made of special alloys. The following is a typical example of 'a cast iron'oi this type:

Per cent Total carbon 3.28 Combined carbon- 2.56 Silicon- .75 Manganese .81 Aluminum 1.05 Chromium .34 Titanium .27 Vanadium .39

other desirable properties are similar to those h ter' b mg physlcal propertles produced by the mtnd above mentioned but which are c arac ized y an increase in the initial or as cast hardness may be produced with compositions within thev following range of proportions: from 2.0 to 4% of carbon, 1% or less of manganese, from 1 to 2% oi. silicon, and as alloying additions up to 1.85% aluminum and from 0.5 to 1.5% chromium, with or without a'small but effective proportion, not exceeding 0.5% of each, of one or both of the elements titanium and vanadium. .The following is a typical example of a cast iron of this type:

Per cent Total carbon 3.06 Combined carbon 1.60 Silicon 1.78 Manganese .78 Chromium 1.32 Aluminum, 1.22 Titanium J .27 Vanadium .38

The cast iron in the example cited possessed in the as cast condition before nitriding a hardness of approximately 500 Vickers-Brinell and after nitriding the same in the presence of ammonia for a period of 50 hours at 500 C. it showed a hardness of 1034 Vickers-Brinell. The cast irons of this group,-while possessing a relatively high hardness in their unnitrided state, nevertheless are susceptible before nitriding or being worked by means of special tools.

The alloys comprised within the two groups above mentioned, are particularly suitable for use in situations where high compressive strength 4.5% of silicon, from 1.5% to 3.5% of chromium,-

1 and high core hardness as well as high resistance to wear are important considerations.

For some purposes, it is not so important that the product shall possessa high strength .and core hardness but it is requisite that it show a high resistance to wear. For such purposes-I find that alloys containing from 2.0 to 4% of carbon, 1% or less of manganese, from 2 to and up to 1.85% of aluminum, with or without a small but effective proportion, not exceeding 0.5% of each, of one or both of the elements titanium and vanadium, possess good nitriding This cast iron before nitriding possessed a hardness of only 300 Vickers-Brinell; after nitriding in the presence of ammonia during a period of 50 hours at 500 C. it showed ahardnessof 950 Vickers-Brinell. I

The alloys of this type may be classed as gray cast irons. machining tools and are characterized by particularly good properties as respects toughness and adherence of the nitrided layer. Cast irons of this type are easy to cast, a feature that recommends them for use in forming articles of complicated shapes.

As might be expected from its known properties, chromium has the effect ordinarily of increasing the initial hardness of the casting with resultant decrease in the machinability. 0n the other hand, by increasing the proportion of silicon, the softness of the casting is increased with out diminishing the nitriding effects producedby the chromium and aluminum additions. Accordingly, I find it advantageous to vary the silicon content with the chromium content when machinable castings are'desired andI preferably adjust the silicon content so that it shall be substantially greater than the chromium content. At the same time by increasing the silicon content of alloys of the type here under consideration, the fluidity of the resulting metal is increased making for greater ease in casting.

They are easily worked by the usual In nitriding articles made from the foregoing alloys, it is advantageous to subject the article to a preliminary heat treatment to bring the metal into the sorbitic state. This result may be ob- '1. An article hardened in its surface portions by; nitriding and consisting of a cast iron alloy having the metallographic structure characteristic of gray cast irons and containing from 2.0 to 4% of carbon, an efiective and substantial proportion of aluminum but not exceeding about 1.85%, from 2.0 to 4.5% or silicon, and from 1.5

to 3.5% of chromium.

2. An article hardened in its surface portions by nitriding and consisting of a cast iron alloy having' the metallographic structure characteristic of gray cast iron and containing from 2.0 to 4% of carbon, an eifectiveand substantial proportion of aluminum but not exceeding about 1.85%, from 2.0 to 4.5% of silicon, from 1.5 to 3.5%

of chromium, and an effective and substantial amount but not exceeding about 0.5% each of the metals titanium and vanadium.

- 3. An article hardened in its surface portions by nitriding and consisting of'a cast 'iron alloy having the metallographic structure characteristic of gray cast irons and containing from 2.0

"to 4% of carbon, an effective and substantial proportion of aluminum but not exceeding about 1.85%, from 2.0 to 4.5% of silicon, from 1.5 to 3.5%

containing about 3.19% of carbon, about 0.80%- of manganese, about 4.10% of silicon, about 2.15%

of chromium and about 0.60% of aluminum.

' MARIE LoUI's ANDRE BABINET. 

